The long term goal of this proposal is to identify those mechanisms involved in the cardioprotective effect of light in the red to near infrared range (630-1,000 nm; NIR). Our laboratory has found that brief exposure (3 min) of dog, rabbit and mouse myocardium to 670 nm wavelength light generated by a light-emitting diode at the point of reperfusion following a 30 minute coronary artery occlusion results in a significant reduction in infarct size. Moreover, striking differences in the mechanisms involved in NIR-mediated cardioprotection have been discovered compared to ischemic or pharmacological postconditioning. This may allow application of NIR for cardioprotection in disease models such as diabetes where pharmacological postconditioning has proven to be ineffective. We propose to test the overall hypothesis that NIR treatment of myocardium, immediately following a prolonged ischemic period, involves the release of nitric oxide (NO) from heme-containing proteins. The resulting, and, importantly, site-specific release of NO targets protective signaling pathways and mitochondrial metabolism. Three Specific Aims will be used to identify the potential contributions of NO containing myoglobin, hemoglobin and/or cytochrome c oxidase to the cardioprotective effect of NIR in the non-diabetic and diabetic mouse. Specific Aim I will investigate the effects of NIR on cellular and tissue preservation and function and on mitochondrial bioenergetics in the diabetic and non-diabetic mouse, and compare the effect with a conventional NO-donor. Specific Aim II will study the release of NO from heme-binding partners using mainly biophysical methodologies in cell-free, cellular and tissue models of reperfusion injury. Specific Aim III will explore the source of NO that is largely responsible for the observed cardioprotective effect of NIR and expand the application of NIR to a non- or minimally-invasive animal model. Throughout this proposal we will make use of relevant murine knockouts that are either commercially available or that we have secured from outside collaborators. The mechanisms responsible for the ability of NIR to attenuate the damage to ischemic myocardium during reperfusion have not been characterized and the results of this work will add significantly to the fields of cardiovascular biology and photobiology. Importantly, the use of NIR for reperfusion injury has the potential for rapid translation to the clinic given its relatively safe profile.